Thermionic valve apparatus



April 28, 1936., H A. EWEN THERMIONIC VALVE APPARATUS Filed July 5, 1933INVENTOR HARRY ALEXANDER EWEN AQRNEY Patented Apr. 28, 1936 PATENT,OFFICE THERMIONIC VALVE APPARATUS Harry Alexander Ewen, Shenfield,England, assignor to Radio Corporation of America, a corporation ofDelaware Application July 5, 1

933, Serial No. 679,052

In Great Britain July 8, 1932 2 Claims.

This invention relates to thermionic Valve apparatus and. moreparticularly to radio and similar transmitter installations employingthermionic valves of high power.

In order that radio transmitters and the like employing thermionicvalves of high power may be operated efficiently, it is very desirableto provide means whereby the voltages applied to the filaments of thevarious valves may be adjusted fairly closely to particular values, itbeing common practice to require to be able to adjust filament voltagein steps of the order of one quarter of a volt per step. It is usual atthe present time to provide for such adjustments by means of rheostats,but it will readily be appreciated that such rheostats are not easy oreconomical to design and manufacture when they are required to controlthe filaments of valves of high power where the filament current is ofthe order of 250 ampers or even more.

The present invention has for its object to meet this difiiculty, andaccording to the said invention filament heating for a high power valvein an installation of .the general character above described is obtainedby means of an electrical generator machine, and the required filamentvoltage control is obtained by controlling the excitation of thegenerator. Accordingly in a high power multi-valve installation inaccordance with this invention there will be provided a plurality ofvalves and a plurality of generators for energization of the filamentsof said valves, there being a separate rheostat for the control of thefield excitation of each generator. Preferably the field excitation forall the generators is obtained from a further generator machine, andpreferably also a reversing switch is associated with the supply linesleading from the last mentioned generator to" the field systems of thefilament heating generators so that by reversing the said reversingswitch the polarity in the filament heating generators may be reversedand thus the polarity applied to the various filaments reversed. Theobject of this provision is to reduce filament wear, it being intendedthat the polarity of the filament supply potential shall be reversed atsuitable intervals for the purpose of minimizing filament wear.

Preferably the generators are designed to have falling characteristicsof suitable shape, so that in the event of short circuit or overload theoutput voltages therefrom will be reduced rapidly and automatically,thus obviating the necessity for providing fuses to guard against shortcircuits.

The invention is illustrated in the accompanying drawing which showsdiagrammatically the invention as applied to a radio transmitter.

Referring to the drawing there is provided a pair of motor driven shuntwound generators ElEZ each of say volts 4 k. w. output, and either beingadapted at will to be connected by means of a switch TS through areversing switch RS to feed energy to a pair of bus-bars EBB to behereinafter referred to as the excitation busbars. The shunt field ESFIor ESFZ of each exciter includes in its circuit a rheostat VCI or V02for voltage control. The filament F of each valve V in the transmitteris heated by current supplied from the armature of a separate heatinggenerator I-IG and these generators, may, for example, be each of 35volts 8.5 k. w. output. All the heating generators are separatelyexcited and each has a control rheostat GR connected in its fieldcircuit. Vt are voltmeters. The field circuits and individual controlrheostats for the heating generators are connected in parallel totheexcitation bus-bars EBB and preferably a further rheostat GCR isincluded in the common field excitation or bus-bar circuit so that byoperation of this further rheostat the field excitation of all theheating generators may be controlled together, individual control beingof course obtained by the individual rheostats CR in the separate fieldcircuits. The heating generators are driven in any convenient way, forexample, by electric motors, a practically convenient arrangement beingto provide one electric motor for two heating generators as indicated.One of the two exciter units acts as a spare. Similarly if desired otherspare generator and. motor units may be provided in association withchange-over switches, whereby they may be connected in circuit foroperation when desired.

Having now particularly described and ascertained the nature of my saidinvention and in what manner the same is to be performed, I declare thatwhat I claim is:

l. A radio transmitter comprising a plurality of high powered thermionicvalves, separate cathode heating generators for each of said valves,separate rheostats connected in the field circuit of the respectivegenerators for controlling the field excitation of each generator and agenerator power supply source, comprising two generators for excitingthe fields of each of said separate cathode heating generators, areversing switch connected to the power supply of the field systems ofthe cathode heating generators and the power supply source, saidreversing switch connected to each power supply generator so that thepolarity of said cathode heating generators may be reversed.

2. A radio transmitter comprising a plurality of high-powered thermionicvalves, a separate cathode heating generator for heating each of saidseparate valves, a rheostat connected in series with the field circuitof each separate cathode heating generator, a plurality of power supplygenerators for exciting the field circuit of each cathode heatinggenerator, means for reversing the polarity applied to each separatecathode heating generator, said means comprising a reversing switchconnecting the field circuit of the separate cathode heating generatorsand the power supply generator, and a separate rheostat for controllingthe excitation of each separate power supply generator.

HARRY ALEXANDER EWEN.

